introducing let-syntax
The let-syntax expander is different in that it doesn't apply a mark to its token trees before expansion. This is used for macro_rules, and it's because macro_rules is essentially MTWT's let-syntax. You don't want to mark before expand sees let-syntax, because there's no "after" syntax to mark again. In some sense, the cleaner approach might be to introduce a new AST node that macro_rules expands into; this would make it clearer that the expansion of a macro is distinct from the addition of a new macro binding. This should work for now, though...
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3 changed files with 30 additions and 3 deletions
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@ -13,7 +13,7 @@
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use lint::LintPassObject;
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use syntax::ext::base::{SyntaxExtension, NamedSyntaxExtension, NormalTT};
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use syntax::ext::base::{IdentTT, ItemDecorator, ItemModifier, BasicMacroExpander};
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use syntax::ext::base::{IdentTT, LetSyntaxTT, ItemDecorator, ItemModifier, BasicMacroExpander};
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use syntax::ext::base::{MacroExpanderFn};
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use syntax::codemap::Span;
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use syntax::parse::token;
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@ -57,6 +57,8 @@ impl Registry {
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IdentTT(ext, _) => IdentTT(ext, Some(self.krate_span)),
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ItemDecorator(ext) => ItemDecorator(ext),
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ItemModifier(ext) => ItemModifier(ext),
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// there's probably a nicer way to signal this:
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LetSyntaxTT(_, _) => fail!("can't register a new LetSyntax!"),
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}));
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}
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@ -264,8 +264,15 @@ pub enum SyntaxExtension {
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/// A function-like syntax extension that has an extra ident before
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/// the block.
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///
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/// `macro_rules!` is an `IdentTT`.
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IdentTT(Box<IdentMacroExpander + 'static>, Option<Span>),
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/// An ident macro that has two properties:
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/// - it adds a macro definition to the environment, and
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/// - the definition it adds doesn't introduce any new
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/// identifiers.
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///
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/// `macro_rules!` is a LetSyntaxTT
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LetSyntaxTT(Box<IdentMacroExpander + 'static>, Option<Span>),
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}
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pub type NamedSyntaxExtension = (Name, SyntaxExtension);
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@ -300,7 +307,7 @@ pub fn syntax_expander_table() -> SyntaxEnv {
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let mut syntax_expanders = SyntaxEnv::new();
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syntax_expanders.insert(intern("macro_rules"),
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IdentTT(box BasicIdentMacroExpander {
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LetSyntaxTT(box BasicIdentMacroExpander {
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expander: ext::tt::macro_rules::add_new_extension,
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span: None,
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},
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@ -484,6 +484,24 @@ fn expand_item_mac(it: Gc<ast::Item>, fld: &mut MacroExpander)
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let marked_tts = mark_tts(tts.as_slice(), fm);
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expander.expand(fld.cx, it.span, it.ident, marked_tts)
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}
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Some(&LetSyntaxTT(ref expander, span)) => {
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if it.ident.name == parse::token::special_idents::invalid.name {
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fld.cx.span_err(pth.span,
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format!("macro {}! expects an ident argument",
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extnamestr.get()).as_slice());
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return SmallVector::zero();
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}
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fld.cx.bt_push(ExpnInfo {
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call_site: it.span,
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callee: NameAndSpan {
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name: extnamestr.get().to_string(),
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format: MacroBang,
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span: span
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}
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});
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// DON'T mark before expansion:
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expander.expand(fld.cx, it.span, it.ident, tts)
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}
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_ => {
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fld.cx.span_err(it.span,
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format!("{}! is not legal in item position",
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